Heterocumulenes insertion reactions

A (pentamethylcyclopentadienyl)iridium chelating guanidinate complex has been conveniently prepared by treatment of [Cp IrCl2]2 with N,N, N"-th-p-tolylguanidine and base in THF at room temperature followed by recrystallization of the green product from toluene and pentane (Scheme 154). Insertion reactions of the product with heterocumulenes (diaryl carbodiimides, aryl isocyanates) have been investigated. It was found that the complex serves as highly active catalyst for the metathesis of diaryl carbodiimides with each other and for the more difficult metathesis of diaryl carbodiimides with aryl isocyanates (cf. Section V.C). ... 

Heterochalcogenides, with chromium, 5, 312 Heterocoupling reactions in olefin cross-metathesis, 11, 181 Pd-catalyzed, alkynes, 8, 274—275 Heterocubanes, reactions, 3, 8 Heterocumulenes in insertion reactions, 1, 107 nickel metallacycle reactions, 8, 103-104 Heterocyclic compounds... 

Braunstein has suggested that precoordination is necessary for heterocumulene insertion [64]. If this suggestion is correct, THF must dissociate from 2a or 2b, or PMe3 from 2o, before insertion can take place. Such a mechanism is supported by the kinetics of the reaction (Eq. 27). The inverse dependence upon [THF] in the rate law (Eq. 28) reflects the reversible dissociation of THF from 2p in Eq. 27 [49]. (The dissociation is an unfavorable, but rapidly maintained, preequilibrium.)... 

The insertion reaction of heterocumulenes can be used to syuthesize carbodiimides having two different substituents. For example, the carbamate 157 derived from an isocyanate and bis(tributyltin)oxide can be reacted with an isothiocyanate to give a carbodiimide 158 with substituents derived from the isocyanate and the isothiocyanate. ... 

Heterocumulenes undergo insertion reactions with numerous substrates. In general, carbodiimides react faster than isocyanates and isothiocyanates, in that order. Insertions of carbodiimides into metal-hydrogen, metal-halogen, metal-mitrogen, metal-oxygen and metal-sulfur bonds are reported. Also insertions of carbodiimides into carbon-hydrogen bonds are known. 

Insertion of imsymmetrical heterocumulenes such as 0=C=X (X = S, NR), into an N-Si bond can produce two different constitutional isomers [8]. In the case of compound 1 and X = NR, R = alkyl or aryl, there is rapid insertion into both N-Si functions and the resulting situation is extremely complex with respect to the configurational (0,N-silylation) and conformational isomerism [5, 8, 10]. In contrast, 0=C=S inserts rapidly into only one N-Si bond of 1, there is no evidence for any second insertion even after several days. The formation of small amounts of pyrazine as oxidation product even under strictly anaerobic conditions suggests some electron transfer reactivity. Spectroscopic [10] and especially the structural evidence given below show that of the two conceivable constitutional isomers [11] of the insertion reaction only the 0-Si bonded species 2 with intact thiocarbonyl function is formed. 

Many of these reactions are thermodynamically controlled and proceed under mild conditions. For heterocumulene insertion, the product has additional conjugative stabilization compared with the reagents, and this provides for a favorable free energy exchange for the reaction [e.g., reaction (c)]. A further driving force often derives from the greater polarity of the insertion adduct over its precursors, and the adduct thus frequently precipitates from solution in a nonpolar solvent (cf. 3). 

Zn(H)(Tpph,Me)], obtained from the reaction of [Zn(F)(Tpph Me)] with Et SiH, and [Zn(OH)(Tpph,Me)] undergo insertion reactions with heterocumulenes. CO, CS2, and RCNS insert into the Zn-H bond giving [Zn(OCH(0))(Tpph Me)], [Zn(SCH(S))(Tpph Me)], and [Zn(SCH(NR))(Tpph,Me)], respectively. [Zn(OH)(Tpph Me)] reacts with RCNS yielding [Zn(SC(0)NHR)(Tpph Me). In the presence of EtOH the reaction of [Zn(X)(Tpph,Me) with RNCS yields [Zn-(SC(NR)OEt)(Tpph Me). These compounds have been characterized by X-ray crystallography, supporting a four-center reaction mechanism proposed for hydrolytic zinc enzymes.145 [Zn(OH)-(Tpph,Me)] reacts with simple aminoacids to form [Zn(AB)(Tpph,Me)]... 

Both the formation of XX as well as the reaction of mercuric fluoride with isothiocyanates are examples of the well-known insertion reaction of heterocumulenes... 

Other electrophilic heterocumulenes (e.g., CS2, RNCO, RNCS, SO2) are also subject to insertion reactions. Accordingly, the insertion of CS2 into the M-N bond in metal dialkylamides produces dithiocarbamate derivatives and the reaction of SO2 with M-C bonds gives sulfinate complexes resulting from either 1,1-insertion [M-0S(0)R] or 1,2-insertion [M-S(R)02]. Rare examples of insertion of dioxygen into Pt-H bonds to generate remarkably stable hydroperoxide derivatives L Pt-OOH have also been reported. 

The reactivity of copper aryloxides towards a variety of heterocumulenes has been investigated. " " Insertion of RNCS (R = Me, Ph) into copper(i) aryloxide bonds has been shown to lead to a variety of A-alkylamino(aryloxy)methanethiolato complexes depending on the natnre of the ancillary hgands. In the absence of any other donor ligation a clnster componnd, [Cn /Li2-SC(=NPh)(OAr) ]6 has been characterized from the insertion of PhNCS into a Cn-4-methylphenoxide bond. " Recently the effect of orf/zo-substitnents upon the oligomerization of Cu(i) complexes formed by insertion of CS2 and PhNCS into Cu-OAr bonds has been carried out. " Some of the insertion reactions have been shown to be reversible. 

Ni-alkyne bonding consists of contributions from both the 77, 7t- and cr,diyl tautomers. This bonding picture helps visualize the insertion reactions with alkynes, alkenes, and CO that result in the formation of metallacycles. Thanks to such insertion reactions, Ni-alkyne species are active intermediates in a number of catalytic applications such as alkyne oligomerization, carbonylation, and insertion of heterocumulenes such as CS2 and GO2. For example, a recent example of a C02-fixation reaction involved the stoichiometric, alkylative or arylative carboxylation of alkynes to give a,(3- and / ,/ -unsaturated carboxylic acids. Ni(0)-alkyne complexes have also been used as pre-catalysts in the addition of hydrosilanes to alkynes. In most cases, monoalkynes react to give the products of m-addition, whereas diynes produce enynes (1,2-addition), allenes (1,4-addition), or 1,3-butadienes (1,2,3,4-addition). ... 

An important issue is the regioselectivity of the insertion reaction in those cases where more than one reaction site is available for carbon dioxide insertion or, more generally, for reaction with the heterocumulene. Cowan and Trogler [112] found that trani-Pt(H)(NHPh)(PCy3)2 reacted reversibly with CO2 to give a carbamate rather than a formate or metallo-acid complex. Other studies have established that... 

Direct addition of CO2 across a Zr-Ir bond leading to stoichiometric reduction of carbon dioxide to formate was shown by Bergman and co-workers.[Gp2Zr(/t-NBu )IrCp ] 766 reacts rapidly with CO2 and heterocumulenes. Insertion of CO2 into an M-H bond, leading to a unique heterobimetallic formato complex and stoichiometric conversion of the formato complex to 766 and Li formate by addition of base, was also demonstrated. Different reactions gave the products listed in Scheme 109 and a possible mechanism for their formation was suggested. 

The electron-rich and cyclically conjugated 8 rr electron system of 1,4-dihydropyrazine can be stabilized in essentially planar conformation by organosilicon substitution at the enamine nitrogen centers [1], In addition to electron transfer [1] and triorganosilyl exchange reactions [2], we have explored the possibility of inserting heterocumulenes X=C = Y into one or both of the N-Si bonds of the compounds 1 in order to functionalize this unusual ring structure [3],... 

The reaction of phosphine (produced in situ from magnesium phosphide and hydrogen chloride in dioxan solution) with 1,5-diketones gives106 the phosphorina-none derivatives (104). Carbonyl compounds and heterocumulenes (e.g. CO2, CS2) insert into the germanium-phosphorus bond of germaphospholans to form derivatives of the germaphosphepin system [e.g. (105)].106>107... 

A third kind of reactivity is related to the silyl substitution mechanism in that it involves an intermediate N-Si bond cleavage. Insertion of heterocumulenes such as CO2 is common for N-M bonds [7], including the -NSiR3 function in 1 or other molecules [8, 9]. We now report the result of the reaction between 1 and the unsymmetrical carbonyl sulfide, 0=C=S. 

Some reactions of oxaziridines with heterocumulenes were described by Japanese authors. Two molecules of diphenylketene can form compounds 19 and 20, inserting the group R—N of the oxaziridine. Formally the reaction may be represented as addition of an a-lactam to either the C=0 or the C=C bond of diphenylketene. Depending on the substituents of the starting oxaziridine, types 19 or 20 predominate. 

Transition-metal-catalyzed hetero-[2 + 2 + 2]-cy-cloaddition of alkynes with carbon—heteroatom multiple bonds, such as isocyanides, carbon dioxide, nitriles, aldehydes, and ketones, provides heteroare-nes and unsaturated heterocycles. This reaction can be categorized into two groups one is the reaction of l,a>-diynes 397 with carbon—heteroatom multiple bonds, and the other is reaction of the alkynes 399, having a carbon—heteroatom multiple bond with alkynes as illustrated in Scheme 127. The reaction of 1,6 -diynes 397 proceeds through formation of the metalacyclopentadiene intermediate 398 followed by insertion of a carbon—heteroatom multiple bond, such as heterocumulenes (route a),189 nitriles (route b),190 and carbonyls (route c).191 On the other hand, the... 

Reactions of [MCls-xMe,] (x = 1, 2 or 3) with heterocumulenes have led to insertions into the M—C bond. lV,lV -Dialkylacetamidinato derivatives were obtained (equation 33). N-Acetamides or N-thioacetamides were formed with isocyanates or isothiocyanates, respectively (equation 34). The rate of insertion varied in the order [MCl4Me] > [MCl3Me2] > [MCl2Me3], following the established order of acceptor properties of the methylmetal chlorides, the isocyanates being more reactive than the isothiocyanates. Hexa- or hepta-coordinated species were obtained. 

An unusual class of Pd-catalyzed [3 + 2] cycloaddition reactions between activated aziridines and heterocumulenes such as isocyanates and carbodiimides has been extensively examined by Alper and coworkers [94]. These transformations led to the preparation of ureas, carbamates, and other heterocydes in good yields. For example, treatment of 138 with phenylisocyanate afforded urea 139 in 72% yield (Eq. (1.55)) [94aj. The mechanism of these reactions presumably involves oxidative addition of the aziridine to Pd , followed by insertion of the isocyanate into the Pd—N bond and C—C bond-forming reductive elimination (similar to the reactions of vinylaziridines described in the section above, although allylpalladium intermediates are obviously not involved). 

Nucleophilic attack at remote positions of coordinated ligands is observed when these are activated by strongly electron-withdrawing groups. For instance, PEts displaces a fluoride atom from complex 131 affording a phospho-niovinyl complex (Equation (66)). A related reaction is the hydrolysis of coordinated 2,4,6-trifluoropyrimidine, to afford a 4,6-difluoropyrimidin-2-one complex. An unusual reaction is the formal insertion (probably electrophilic attack) of heterocumulenes (GS2 or CO2) into a coordinate Ni-P bond of 70 (Equation (67)). 

Carbon dioxide can also form carbamates by reaction with amides of non-metallic elements [78-84, 136-144]. Most examples reported in the literature deal with amides of silicon, germanium, and phosphorus. Among these, the insertion of the heterocumulene into the P-N bond of hexaalkylphosphorus triamides P(NR2)3, which affords phosphocarbamates species of formula P(NR2)3 (02CNR2) t, has received particular attention for its potential in chemical synthesis, because this reaction opens a route to the phosgeneless synthesis of carbamate esters [138,139] and ureas [140]. 

The mechanism through which the metathetical reaction is beUeved to occur with M[N(SiMe3)2]2 (M = Ge, Sn) amides is shown in Scheme 4.26 [145]. The initial insertion step of the heterocumulene into the M-N bond is apparently followed by a facile molecular... 

Yasuda H, Okamoto T, Matsuoka Y, Nakamura A, Kai Y, Kanehisa N, Kasai N (1989) Diverse reaction courses in the controlled carbometalation of heterocumulenes with zirconium-diene complexes and molecular structures of carbon dioxide, isocyanate and ketene 1 1 and 1 2 inserted compounds. Organometallics 8 1139-1152... 

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